A first subject matter of the invention is an electric machine comprising the following features:
(a) an outer, first stator part and an inner, second stator part, the two stator parts being coaxial and being radially spaced apart by an intermediate space;
(b) each stator part has, facing the intermediate space, a circumferential series of stator poles, at least a partial number of which carries a winding;
(c) a rotor part disposed in the intermediate space;
(d) the rotor part has a circumferential series of alternating permanent magnets and magnetic flux conducting pieces, said permanent magnets being magnetized in circumferential direction;
(e) the width of the permanent magnetsxe2x80x94measured in circumferential directionxe2x80x94is larger on the central radius of the rotor part than radially outside and radially inside on the rotor part and the width of the magnetic flux conducting piecesxe2x80x94measured in circumferential directionxe2x80x94is correspondingly smaller on the central radius of the rotor part than radially outside and radially inside on the rotor part;
(f) a first circumferential series of magnetic circuits whichxe2x80x94as seen in a plane perpendicular to the rotor axisxe2x80x94each extend through two adjacent stator poles of the first stator part in the plane considered and through two adjacent magnetic flux conducting pieces of the rotor part in the plane considered and through the permanent magnet between the two adjacent magnetic flux conducting pieces in the plane considered, and a second circumferential series of magnetic circuits whichxe2x80x94as seen in a plane perpendicular to the rotor axisxe2x80x94each extend through two adjacent stator poles of the second stator part in the plane considered and through two adjacent magnetic flux conducting pieces of the rotor part in the plane considered as well as through the permanent magnet between the two adjacent magnetic flux conducting pieces in the plane considered.
A second subject matter of the invention is an electric machine comprising the following features:
(a) a first stator part and a second stator part, the two stator parts being arranged along a common axis and being axially spaced apart by an intermediate space;
(b) each stator part has, facing the intermediate space, a circumferential series of stator poles, at least a partial number of which carries a winding;
(c) a rotor part disposed in the intermediate space;
(d) the rotor part has a circumferential series of alternating permanent magnets and magnetic flux conducting pieces, said permanent magnets being magnetized in circumferential direction;
(e) the width of the permanent magnetsxe2x80x94measured in circumferential directionxe2x80x94is larger in the axially central portion of the rotor part than at the axial faces of the rotor part and the width of the magnetic flux conducting piecesxe2x80x94measured in circumferential directionxe2x80x94is correspondingly smaller in the axially central portion of the rotor part than at the axial faces of the rotor part;
(f) a first circumferential series of magnetic circuits whichxe2x80x94as seen in a developed circumferential areaxe2x80x94each extend through two adjacent stator poles of the first stator part in the circumferential area considered and through two adjacent magnetic flux conducting pieces of the rotor part in the circumferential area considered and through the permanent magnet between the two adjacent magnetic flux conducting pieces in the circumferential area considered, and a second circumferential series of magnetic circuits whichxe2x80x94as seen in a developed circumferential areaxe2x80x94each extend through two adjacent stator poles of the second stator part in the circumferential area considered and through two adjacent magnetic flux conducting pieces of the rotor part in the circumferential area considered as well as through the permanent magnet between the two adjacent magnetic flux conducting pieces in the circumferential area considered.
The electric machine according to the second subject matter of the invention differs from the electric machine according to the first subject matter of the invention in that the two air gaps (one air gap between the first stator part and the rotor part and a second air gap between the rotor part and the second stator part) are in two planes perpendicular to the rotor axis, whereas in the first subject matter of the invention there are provided two circumferential air gaps in radially spaced apart manner.
The electric machines according to the invention distinguish themselves by very high power density. This results from the presence of two stator parts and a common rotor part therebetween, but also from the geometry indicated of the magnetic flux conducting pieces and the permanent magnets. In addition thereto, the mutual xe2x80x9cself-anchoring effectxe2x80x9d of the components of the rotor parts is to be emphasized.
The electric machines according to the invention in particular may be machines outputting mechanical power (i.e. electric motors) or machines taking up mechanical power (i.e. generators). They are preferably electronically commutated electric motors or generators with take-off of electric power via active current converters.
In the first subject matter of the invention, the width mentioned of the magnetic flux conducting pieces radially inside on the rotor part and radially outside on the rotor part each is preferably smaller than the radial dimension of the particular magnetic flux conducting piece. In the second subject matter of the invention, the width mentioned of the magnetic flux conducting pieces on the axial faces of the rotor part each is analogously preferably smaller than the axial dimension of the particular magnetic flux conducting piece. This measure in both cases has the effect that the rotor part is designed in accordance with the magnetic flux concentration principle, i.e. a higher magnetic flux density is present at the exit of the magnetic flux conducting pieces to the corresponding air gap than in the respective magnetic flux generating permanent magnet.
In case of the first subject matter of the invention, the rotor part preferably is a constituent part of a cup-shaped portion of the rotor. In this case, the rotor can be designed so as to be supported on one axial side of the machine only, which has practical advantages for many fields of application.
Preferably, the cup-shaped portion of the rotor has a rotor base wall and the rotor part is mounted to the base wall via circumferentially distributed tie rods, with the tie rods being mounted on the one hand on the base wall and on the other hand extending through bores in the magnetic flux conducting pieces and/or the permanent magnets. This way of mounting by means of tie rods is particular advantageous in terms of production technology. It is pointed out that, due to the geometry mentioned of the permanent magnets and the magnetic flux conducting pieces, it is basically sufficient to directly fix either only the magnetic flux conducting pieces or the permanent magnets by means of the tie rods, since the respective other constituent parts, permanent magnets/magnetic flux conducting pieces, are held indirectly via positive engagement. On the other hand, it is indeed possible as well to secure both constituent parts, i.e. permanent magnets and magnetic flux conducting pieces, to the rotor base wall by means of tie rods each.
The magnetic flux conducting pieces and/or the permanent magnets may be subdivided, in the direction of the rotor axis, into a plurality of electrically isolated sections, which is preferred. These sections preferably can be adhesively joined to each other and/or be held together by tie rods. This reduces eddy current losses.
The magnetic flux conducting pieces and the permanent magnets preferably are subdivided, in the direction of the rotor axis, into a plurality of sections which are separated by intermediate rings of magnetically non-conducting material, which best should be electrically non-conducting as well. By means of this construction, it is possible to build rotor parts with increased mechanical strength. Between the respective intermediate rings, the magnetic flux conducting pieces and/or the permanent magnets may be further subdivided more finely into subsections which are electrically isolated from each other. It may be advantageous in certain designs to adhesively join magnetic flux conducting piece sections and/or permanent magnet sections to the intermediate rings, in particular if these are not held directly by tie rods.
The intermediate rings preferably are of smaller outer diameter than the magnetic flux conducting pieces and the permanent magnets and/or of larger inner diameter than the magnetic flux conducting pieces and the permanent magnets. This provides for advantages in terms of adhesion technology and for an improved design of the inner and outer surfaces of the rotor part.
The rotor part, on the outside thereof, preferably is provided with a circumferential strengthening bandage that preferably has a thickness of less than 1.5 mm. The strengthening bandage is capable of relieving the structure of the rotor part of a considerable portion of the centrifugal forces arising. Due to the fact that the strengthening bandage is located in the radially outer air gap, the thickness thereof should be as small as possible. A preferred material for the strengthening bandage is plastics material reinforced with carbon fibers.
Analogously therewith, the rotor part of the second subject matter of the invention preferably is a constituent part of a disc-shaped portion of the rotor. Advantages in terms of manufacturing technology are obtained here too. Preferably, the rotor part is provided on its outside with a circumferential strengthening bandage. In case of the second subject matter of the invention, the thickness of the strengthening bandage can be chosen more freely as said bandage is not disposed in an air gap.
In case of both subject matters of the invention, the number of stator poles on the first stator part preferably is equal to the number of stator poles on the second stator part. In addition thereto, it is preferred in this context that each stator pole on the first stator part has located opposite thereto, beyond the rotor part, a stator pole on the second stator part with the same electromagnetic phase position, as one moves (with respect to the first subject matter of the invention) along a radius in inward direction, and (with respect to the second subject matter of the invention) along a line parallel to the rotor axis, respectively. These measures result in optimum magnetic flux exploitation and in a desirable symmetry of the magnetic fluxes.
The following holds for both subject matters of the invention: preferably, the first stator part and/or the second stator part is provided with direct cooling by fluid flow along the windings; preferably, the first stator part and/or the second stator part is provided with stator back cooling. In case of direct cooling by fluid flow, the area containing the stator pole ends is sealed in fluid-tight manner on all sides e.g. by a closure member, such as a strong film material. It is then possible to flow a cooling fluid through the channels between two adjacent stator poles each, with said channels being filled to a considerable part by winding wires. As an alternative or in addition thereto, cooling fluid channels can be provided in the stator poles. Suitable cooling fluids are first of all liquids, but gaseous cooling media are possible as an alternative as well.xe2x80x94The additional preferred possibility consists in more indirect stator back cooling, in particular with cooling fluid channels for liquid or gaseous cooling fluid in or on the stator back. However, it is also possible to cool the surface of the stator back facing away from the air gap with cooling liquid or gaseous cooling fluid.xe2x80x94In case of the first subject matter of the invention, a design with direct liquid cooling along the windings on the second stator part and with stator back cooling on the first stator part is particularly preferred.
In case of the first subject matter of the invention, the first stator part and the second stator part preferably are mounted on a common stator base wall; a closed housing in the conventional sense often is no longer necessary at all. On or in the stator base wall, there may be applied preferably a coolant supply as well as electric power and control lines and, if desired, also the electronic system provided for operation of the machine.
In accordance with an alternative design, preferably the first stator part and the second stator part are each mounted separately on the supporting part of the machine, preferably the machine housing.
In both subject matters of the invention, it is preferably provided that at least one active inverter electronics system is connected to the coils of the machine. In case of an electric motor, the inverter electronics system provides for the electronic commutations of the coil currents and, optionally, for power control and, optionally, speed control of the electric motor.
In case of a current generator, there is preferably provided a rectifier means connected to the windings of the machine for generating direct current by means of the current generator. In the simplest case, this may be a passive rectifier. More preferable is a controlled rectifier operating e.g. according to the principle of phase-angle control. Most preferred are active rectifiers. These may be composed like inverters in terms of electronics. They may have the function of delivering an adjustable voltage and/or the function of delivering a voltage that is substantially independent of the speed.